Parallel optical transceiver modules typically include a plurality of laser diodes for generating optical data signals, laser diode driver circuitry for driving the laser diodes, a controller for controlling operations of the transceiver module, receiver photodiodes for receiving optical data signals, receiver circuitry for demodulating and decoding the received optical data signals, and monitor photodiodes for monitoring the output power levels of the laser diodes. Parallel optical transceiver modules typically also include an optical subassembly having optical elements that direct the optical data signals produced by the laser diodes onto the ends of optical fibers and that direct optical data signals received over optical fibers onto the receiver photodiodes.
The laser diode driver circuitry is typically contained in an integrated circuit (IC) having electrical contacts pads that are electrically coupled by electrical conductors (e.g., bond wires) to electrical contacts pads of the laser diodes. The number of laser diodes that are included in a parallel optical transceiver module depends on the design of the module. A typical parallel optical transceiver module may contain six laser diodes and six receiver photodiodes to provide six transmit channels and six receive channels. A typical parallel optical transceiver module that has no receiver photodiodes (i.e., an optical transmitter module) may have, for example, twelve laser diodes for providing twelve transmit channels. The laser diode driver ICs that are commonly used in these types of parallel optical transceiver or transmitter modules generate large amounts of heat that must be dissipated in order to prevent the laser diodes from being adversely affected by the heat. Due to the large amounts of heat generated, the tasks associated with designing and implementing a suitable heat dissipation system are challenging.
In addition, in a typical parallel optical transceiver or transmitter module, the laser diode driver IC is typically placed in very close proximity to the laser diodes to enable the bond wires that couple the contact pads of the laser diodes to the contact pads of the driver IC to be kept relatively short. Long bond wires can lead to electromagnetic coupling between adjacent bond wires that can degrade signal integrity, thereby detrimentally affecting the performance of the module. Placing the driver IC in close proximity to the laser diodes and using relatively short bond wires makes designing and implementing a suitable heat sink solution for the module even more challenging.
The heat dissipation systems used in existing parallel optical transceiver and transmitter modules typically comprise a heat sink structure that is mechanically and thermally coupled to a lower surface of a leadframe of the module. The laser diodes and laser diode driver IC are mounted on an upper surface of the leadframe. The coupling of the heat sink structure to the lower surface of the leadframe provides a thermal path for heat dissipation that is: from the laser diodes and driver IC down into the upper surface of the leadframe; from the upper surface of the leadframe through the leadframe to the lower surface of the leadframe; and then from the lower surface of the leadframe into the heat sink device secured thereto. The heat sink structure is typically a generally planar sheet of thermally conductive material, such as copper or aluminum. A thermally conductive material or device is used to secure the heat sink structure to the lower surface of the leadframe. As an alternative to using a generally planar heat sink structure secured to the lower surface of the leadframe, one or more heat sink devices may be coupled to other locations on the leadframe, such as to the side edges of the leadframe. In the latter case, heat that is transferred into the leadframe is transferred to the side edges of the leadframe and into the heat sink devices. In this type of arrangement, the leadframe functions in part as a heat spreader device to move heat generated by the laser diodes and laser diode driver IC away from those devices and then, via the heat sink devices coupled to the side edges of the leadframe, out of the leadframe.
One of the problems associated with the heat dissipation systems described above is that they do not protect the laser diodes and the laser diode driver IC from particulates, such as dust, for example. In fact, the process of securing the heat dissipation system to the leadframe may result in dust or other particulates being deposited on the laser diodes, which can degrade their performance. Additionally, some amount of handling typically occurs during the process of mounting the module on the PCB, which can lead to the laser diodes, the laser diode driver IC, bond wires, and other components of the module being damaged. Thus, while the customer's heat dissipation system may be effective at dissipating heat, it typically does not protect the laser diodes and ICs of the module from dust and other particulates or from mechanical handling forces that can damage these components.
Accordingly, a need exists for a parallel optical transceiver module having a heat dissipation system that is capable of dissipating large amounts of heat and that protects the laser diodes and other components of the module from particulates, such as dust, for example, and from mechanical handling forces.